Patients who require frequent infusion therapy often opt to have a subcutaneous vascular access port surgically implanted. These ports generally contain a tough, self-sealing septum which is positioned just below the skin. The tough septum is permanently compressed and held in a rigid access port housing which is sutured directly to muscle tissue to prevent movement. The housing confines a sealed reservoir directly beneath the septum. The housing is typically made of titanium, stainless steel, DELRIN.RTM. acetal resin, polysulfone or some other biocompatible and drug compatible material. The reservoir communicates with a vein or artery by way of a silicon or polyurethane connector tube. Although most commercial subcutaneous access port systems share these common elements, a variety of different configurations have been proposed. For a further discussion of subcutaneous access port devices see: Foltz, Evaluation of Implanted Infusion Devices, NITA, Vol. 10, No. 1, pp. 49-51 (1987); Goodman et al., Venous Access Devices--An Overview, Oncol. Nurs. Forum, Vol. 11, No. 5, pp. 16-23 (1984); and, May et al., Percutaneous Catheters and Totally Implanted Access Systems, Journal of Intravenous Nursing, Vol. 11, No. 2, pp. 97-103 (1988), incorporated herein by reference.
In practice, a doctor or nurse palpates the skin to find the outer perimeter or rim of the implanted port septum and then inserts a rigid, metal hypodermic needle directly through the skin and through the septum until the bottom of the reservoir is reached. At this point, infusion therapy is initiated. When the needle is removed the septum self-seals.
The self-sealing septa used in these devices are very tough and typically from about 0.200 inches to about 0.500 inches thick. These septa are required to be tough enough to withstand thousands of punctures with a 19, 20, 21 or 22 gauge hypodermic needle and still maintain an effective seal.
Other subcutaneous medical devices utilizing this type of tough, self-sealing septa include hydrocephalus shunts, dialysis grafts and artificial organs; all of which require intermittent introduction and/or removal of fluid material. These septa are typically mounted in a port housing similar to the subcutaneous vascular access port described above.
The use of rigid, stainless steel hypodermic needles in subcutaneous access port applications has several shortcomings. First, hypodermic needles inserted in port septa are very uncomfortable for the patient, particularly for extended infusion regimes. Second, the hypodermic needle tends to rock and move with body motion. This movement can result in the needle dislodging. If the needle partially dislodges, blood or infused liquid is pumped beneath the skin which can cause tissue damage and an increased risk of infection. If the needle totally dislodges, the liquid could contaminate the surrounding area. Furthermore, needle movement can lead to severe septum damage and subsequent leakage. Third, tissue damage can result from the rigid nature of the hypodermic itself.
One attempt to alleviate these problems involves using "L"-shaped, right-angle needles, like the ones found in FIGS. 1 and 2. Unfortunately, the length of the needle arm from the tip to the elbow of the needle must vary from patient to patient.--Obese patients will require deep penetration (FIG. 1), while thinner patients will require shallower penetration (FIG. 2).--Accordingly, healthcare facilities must keep a variety of right-angle needle sizes on hand to accommodate a variety of patient types. Furthermore, the correct right-angle needle size can only be determined by trial and error, often requiring several applications before the healthcare practitioner determines the optimal depth of penetration for a given patient. This practice is still further complicated by the fact that many patients who require infusion therapy often undergo dramatic changes in weight; thus, requiring the healthcare practitioner to reevaluate the correct needle size with every patient visit.
Another shortcoming of rigid needles in general is that they require extensive dressing with gauze and tape or, in the alternative, require a very specialized and expensive infusion set to prevent the dislodging effect described above.
Some have attempted to develop more comfortable, flexible catheters for subcutaneous access ports. One example is Titan Medical's SURECATH.TM. port access system product which utilizes an elaborate needle inserting device to anchor and insert the flexible tube to the port. This device is described in U.S. Pat. No. 5,135,502 to Koenig, Jr. et al. This device is difficult to use and involves an expensive inserting device.
It is therefore an object of the present invention to provide an improved catheter for subcutaneous access ports which is relatively inexpensive and simple to use, and which overcomes one or more of the above mentioned problems.
Another object is to provide a catheter which incorporates a pretensioned, helical coil in a flexible cannulated portion. This feature allows the flexible tube to be bent without kinking under normal use. The flexible nature of the tube also is significantly more comfortable than conventional rigid catheters. Furthermore, pretensioning the coil helps keep the catheter longitudinally stiff when a puncture needle is positioned axially down the length of its cannula. This stiffness is essential to facilitate needle penetration through the tough, self-sealing septum used in subcutaneous access ports.
These and other objects will be evident to one skilled in the art from the following: